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Direct Inoculation of Five-Needle Pines with Cronartium ribicola in Axenic Culture. Alex M. Diner, Department of Botany, North Carolina State University, Raleigh 27650; Ralph L. Mott, Department of Botany, North Carolina State University, Raleigh 27650. Phytopathology 72:1181-1184. Accepted for publication 9 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1181.

Vegetative hyphae of Cronartium ribicola grown in axenic culture frequently penetrated the thin cuticle of hypocotyls of cultured Pinus lambertiana embryos without formation of appressoria. Hyphae penetrated the epidermal cells directly or entered between anticlinal walls and branched in the outermost cortical layer. In a few cases, vegetative hyphae entered stomates either with or without formation of an appressoriumlike structure. Vesicle formation in the substomatal cavity, although typical of natural penetration of the host in the field, was not observed in our materials. Thus, the typical, natural entry through stomates may represent the only penetration pathway available to germinal hyphae on needles otherwise protected by a thick cuticle.

Additional keywords: blister rust, sugar pine, western white pine, white pine.